Physiological and Ecological Studies on an Arctic Vegetation: II. The Development of Vegetation in Relation to Nitrogen Supply and Soil Micro- Organisms on Jan Mayen Island

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Abstract
II. N deficiency is the most important factor in determining the distribution and development of the various communities. In barren areas or where the vegetation is sparse and stunted the level of organic and of inorganic N in the soil is minimal and few spp. of microorganisms are present. Closed communities with a dense vegetation and a rich soil population of bacteria and protozoa are only found in localities where the N supply is increased by mammal and bird excreta. The level of inorganic N compared to that of soils in temperate regions is everywhere very low and is probably associated with a slow rate of bacterial activity due both to the prevailing low temps. and the lack of available nutrients.[long dash]III. During the growing season there is a considerable accumulation of sugars and starch in the leaves and roots of Oxyria digyna and Polygonum viviparum and even in the spring when vegetative development is most rapid the carbohydrate content remains high. The net assimilation rate of detatched leaves of O. digyna was 0.3 g. per sq. dm. per week and undetached leaves exhibited significant diurnal changes in the starch and sugar levels. Field expts. showed that the stomata of O. digyna and Taraxacum croceum were continuously open but the aperture was greater when during the day the light intensity and temp. were maximal. Evidently C assimilation does not limit the growth of arctic plants; rather the slow growth rate is controlled by low temp., exposure and in particular N deficiency.